1. Technical Field of the Invention
The present invention relates to detection of an electromagnetic wave (frequency thereof is equal to or more than 0.01 [THz], and equal to or less than 100 [THz]) (such as a terahertz wave (frequency thereof is equal to or more than 0.03 [THz], and equal to or less than 10 [THz]), for example).
2. Related Art
As a method for detecting a temporal waveform of a terahertz wave pulse, there is an EO (electro-optic) sampling method using electro-optic crystal (refer to a Non-patent Document 1 and a Non-patent Document 2).
According to the EO sampling method described in the Non-patent Document 1, probe pulse light and a terahertz wave to be measured are collinearly (coaxially) made incident to the electro-optic crystal. The incident probe pulse light generates a phase difference between an a axis and a b axis due to an electro-optic effect by an electric field of the terahertz wave, and the terahertz wave is detected by detecting the phase difference.
According to the EO sampling method described in the Non-patent Document 2, a terahertz wave is made incident to the electro-optic crystal at an angle θ (0<θ<90°) with respect to probe pulse light. Cherenkov phase matching is generated in the electro-optic crystal, and an electro-optic effect by an electric field of the terahertz wave generates a phase difference between the a axis and the b axis in the incident probe pulse light. The terahertz wave is detected by detecting this phase difference.
According to the EO sampling methods according to prior art described above, influence of a large birefringence of the electro-optic crystal is not negligible. The probe pulse light extracted from the electro-optic crystal is transmitted through a quarter-wavelength plate, is reflected by an mirror, is again transmitted through the quarter-wavelength plate, and is returned to the electro-optic crystal, thereby cancelling the influence of the large birefringence of the electro-optic crystal.
(Non-patent Document 1)
“Use of the organic crystal DAST for terahertz beam applications”, P. Y. Hans et. al., (May 1, 2000/Vol. 25, No. 9/OPTICS LETTERS)
(Non-patent Document 2)
“Efficient electro-optic sampling detection of THz wave with Cherenkov-type phase matching,” Kazuki Horita, Tetsuya Kinoshita, Christopher T. Que, Michael Bakunov, Kohji Yamamoto, and Masahiko Tani, International Symposium on Frontier of Terahertz Spectroscopy IV:, Innovations in THz Spectroscopy and THz-Wave Wireless Communications Japan, Poster paper P-3 (Oct. 20th-23rd, 2010, Matsumoto Campus, Shinshu University, Matsumoto, Japan)